This IS all very interesting. I always wondered how it all comes together. My thought was "why all the horsepower" when its NOT direct drive and its using electrical traction motors. Im like "ALL it needs to do is turn the alternator/generator over to make electric....a 15hp Briggs and Stratton could do that"...
I don't think your 15 hp Briggs and Stratton could even rotate the main alternator with the locomotive loading light in notch 1. The higher the horsepower the more torque and work the diesel engine can provide. The previous poster was under the impression that diesel engine on locomotives bog down when the locomotive is under load. The fact is, the governor maintains the diesel engine RPM at full load, it does not bog down and that is why the control systems monitor the current draw. If the diesel engine cannot provide the horsepower needed, because of an issue, the load regulator backs off the main alternator output. As the traction motors begin to stall going up a grade, the current increases. The governor maintains horsepower and the Main Alternator keeps supplying more current and voltage to the traction motors. You've probably heard the term "Short Term Rating" meaning when the traction motors are drawing 1,500 amps, you can only allow them to do so for a very short period of time as the motors begin to overheat. Once the motors begin to over heat, you start burning open field coils or traction motor leads. The diesel engines on both EMD and GE products never bog down, unless there is a problem with the diesel engine. GE's are unique, in the fact that you can loose power assemblies and the engine governing unit will just increase the fuel pressure to the other cylinders to maintain horsepower. Once you've lost 4 power assemblies on a GE (dash 9, newer EVO's only have 12 cylinders) then it starts to de-rate the horsepower. On a EMD 710-16 rated at 4,000 hp, you need every power assembly to produce 250 hp, if you loose one power assembly, you'll drop 250 hp. On a 645-16 rated at 3,000 hp it's 187 hp per power assembly. Now you may wonder how the main alternator controls it's current and voltage output? The main alternator has gated diodes that control the field. The longer you keep those diodes turned on, the more field voltage is produced which in turn produces more current and voltage output. These locomotives are very interesting machines and have come a long way since the days of Main DC Generators and relay logic to control the traction system.
Indeed they have. It's much more than just high boost and intercooling which is boosting output and efficiency and smoothing out operation. Thanks for the peek inside the hood of the modern marvels.
